Synthesis and reactivity of heterometallic RhO–M (M = Si, Ti) complexes: Memory effect in their catalytic performance in CO hydrogenation

The titanium salycilate complex [Cp*Ti(sal)(salH)] 1 (salH2 = salycilic acid) was synthesised by reacting Cp*TiMe3 and salycilic acid. The molecular structure of 1 studied by X-ray shows it to be dinuclear with a carboxylate group acting as a bridge ligand. [Rh(μ-OH)COD]2 reacts with 1 to yield the bimetallic complex 2, or with the siloxanodiol (HOSiPh)2O to yield the bimetalic bis-siloxide Rh complex 3. Carbon monoxide displaces COD in 2 and 3 to give the carbonylic complexes 4 and 5 respectively. Complex 4 can also be prepared from 2 and [Rh(acac)(CO)2]. Compounds 2, 3, 4 and 5 can be envisaged as models of Rh complexes anchored on titania or silica. The catalytic performance of heterometallic complexes is studied in the CO hydrogenation reaction and compared to rhodium-based (Rh-based) catalysts prepared by impregnation from Rh(NO3)3 or [Rh(acac)(CO)2] showing higher yields to oxygenated products.

Graphical abstractThe heterometallic Rh–titanium salycilate and Rh–siloxide complexes were tested in the CO hydrogenation reaction showing higher yields to oxygenated products referred to Rh-based supported catalysts prepared by conventional methods. Figure optionsDownload full-size imageDownload as PowerPoint slide